1. Field of the Invention
The present invention relates to a positioning apparatus, exposure apparatus, and device manufacturing method used for, for example, a semiconductor manufacturing apparatus.
2. Description of the Related Art
One index of the performance of a semiconductor manufacturing apparatus is the throughput which indicates the number of wafers it can process per unit time. To attain a high throughput, a scanner exposure apparatus, in particular, is required to move a reticle stage which supports a reticle master at high speed by increasing the acceleration/deceleration. However, the acceleration schemes using conventional linear motors lead to high power consumption and high driver output voltage.
Under the circumstances, Japanese Patent Laid-Open No. 2004-79639 proposes a technique of arranging large-thrust acceleration repulsion magnets at the two ends of the stage to perform high-accuracy control using a control linear motor while suppressing electric current consumption upon acceleration.
FIGS. 6A and 6B show an arrangement of a conventional positioning apparatus. FIG. 6A is a plan view of the conventional positioning apparatus, and FIG. 6B is a front view. In this positioning apparatus, a base guide 102 is fixed to a main body base 101, and a stage 104 which mounts a processing object 103 is supported to be movable in one axial direction with respect to the base guide 102.
A bearing 114 inserted between the upper surface of the base guide 102 and the lower surface of the stage 104 regulates the orientation of the stage 104. Linear motor movable elements 105 are fixed to both sides of the stage 104. A linear motor stator 106 faces the linear motor movable element 105 in a noncontact manner and is fixed to the main body base 101. The position of the stage 104 is measured by irradiating a reflection mirror 117 with a laser beam from a laser interferometer.
This positioning apparatus comprises repulsion magnet units each having a detailed arrangement as shown in FIG. 7. Repulsion movable elements 107 each including a movable magnet holder 108 and movable magnet 109 are fixed at the front and back ends of the stage 104. The movable magnet 109 is a plate-like unipolar permanent magnet magnetized in the vertical direction. In this prior art, the upper surface of the movable magnet 109 is magnetized into an N pole. The repulsion movable element 107 acts as an inserted magnet which interacts with a repulsion stator 110 arranged on the base guide 102 to apply a repulsion force to the stage 104, thereby accelerating/decelerating the stage 104.
A characteristic feature of the above-described arrangement of the repulsion magnet unit is that the direction in which it generates a repulsion force is perpendicular to the magnetization direction of the permanent magnet. For example, even when identical poles of magnets magnetized in the Y direction are set to face each other, it is possible to obtain a repulsion force in the Y direction. In this case, however, the distance along which the repulsion magnet unit can generate a repulsion force is too short to attain a sufficiently high speed. In contrast, as shown in FIG. 7, a pair of magnets of the same polarity are set to face each other to utilize a force generated in a direction perpendicular to the direction they face each other. This makes it possible to obtain a force generation stroke corresponding to the sizes of the pair of magnets of the same polarity which face each other. In addition, the repulsion magnet unit has a structure in which upper and lower magnets 112 sandwich the respective pole faces of the movable magnet 109 from both sides. This makes it possible to cancel a repulsion force in the direction they face each other.
The repulsion stators 110 which apply an acceleration/deceleration force to the stage 104 are fixed on the base guide 102 in correspondence with the repulsion movable elements 107. The repulsion stator 110 is set at each edge of the stroke region of the stage 104. The repulsion stator 110 acts as a magnet group including an upper yoke 111, the upper magnet 112, two side yokes 113, the lower magnet 112, and a lower yoke 111. The upper and lower magnets 112 are plate-like unipolar permanent magnets magnetized in the vertical direction, like the repulsion movable element 107. The poles of the upper and lower magnets 112 face identical poles of the repulsion movable element 107. That is, the lower surface of the upper magnet 112 corresponds to an N pole, while the upper surface of the lower magnet 112 corresponds to an S pole. The upper yoke 111, side yokes 113, and lower yoke 111 are provided so that the magnetic fluxes of the upper and lower magnets 112 run through them sideways.
The interval between the upper and lower magnets 112 is slightly larger than the thickness of the movable magnet 109, while that between the two side yokes 113 is wider than the width of the movable magnet 109. The movable magnet 109 can be inserted into a hole in a noncontact manner, which is formed among the pair of upper and lower magnets 112 and two side yokes 113.
A method of accelerating the stage 104 will be explained next. First, the linear motors 105 and 106 accelerate the stage 104 in, for example, the +Y direction while no repulsion force of the repulsion magnet unit acts on the stage 104, that is, while the repulsion movable element 107 is not inserted in the repulsion stator 110. As the stage 104 gradually picks up speed using the linear motors 105 and 106, it reaches the repulsion force acting region of the repulsion magnet unit. At this point, the repulsion movable element 107 starts to be inserted into the repulsion stator 110 so that the repulsion magnet unit begins to accumulate a repulsion force in the −Y direction. An electric current which acts against the repulsion force flows through the linear motors 105 and 106.
In this state, when the electric current flowing through the linear motors 105 and 106 is set to zero, the stage 104 accelerates in the −Y direction upon receiving the repulsion force. As the repulsion movable element 107 is pushed out of the inserted position upon receiving the repulsion force in the direction indicated by an arrow A, the repulsion force decreases. When the repulsion movable element 107 sufficiently separates from the repulsion stator 110, the repulsion force becomes zero. Since the stage 104 accelerates to a maximum speed corresponding to the amount of insertion and is guided by the bearing 114, it moves to the opposite side while keeping this speed. The stage 104 then reaches the repulsion force acting region of the repulsion magnet unit on the opposite side. The kinetic energy of the stage 104 is conserved until the repulsion movable element 107 on the opposite side of the stage 104 interacts with the repulsion stator 110 at the other end. Hence, the speed of the repulsion movable element 107 on the opposite side of the stage 104 also becomes zero while it is inserted into the repulsion stator 110 at the other end by the same amount of insertion as that of the first time.
The linear motors 105 and 106 accelerate the stage 104 in the −Y direction while it further moves in the −Y direction. This makes it possible to further increase the amount of insertion of the repulsion movable element 107 in the repulsion stator 110 than that of the first time. That is, the repulsion magnet unit can accumulate a repulsion force in the +Y direction, that is larger than that of the first time.
In this way, the stage 104 reciprocates a plurality of number of times with acceleration to gradually increase the insertion amount, that is, the repulsion force. Upon eventually achieving a desired amount of insertion, the repulsive acceleration unit will have accumulated a desired repulsion force to actuate the stage 104 at a desired acceleration force.
Unfortunately, the above-described conventional positioning apparatus poses the following problems.
That is, to apply a maximum acceleration force from the repulsion magnet unit to the stage, it is necessary to gradually increase the acceleration force by a plurality of number of times of reciprocating actuation. This disturbs an improvement of the throughput. To accumulate the repulsion force of the repulsion magnet unit only by the forces of the linear motors, they require large thrusts. In particular, a high-acceleration linear motor for, for example, an exposure apparatus must be of not a coreless type but a core type. However, the core type linear motor suffers cogging owing to the positional relationship between the magnet and the core. This cogging acts as a disturbance in a stage control region which requires fine positioning, resulting in a failure in obtaining a fine positioning characteristic. Still worse, the core type linear motor increases the apparatus size and generates high heat.